Silsesquioxane is a general term for a series of network-like polysiloxanes with a ladder, cage, or three-dimensional network (random) structure. Unlike silica, which is a complete inorganic material represented by general formula SiO2, silsesquioxane is soluble in general organic solvents; therefore, it is easy to handle, and processability and moldability during membrane formation etc. are excellent.
On the other hand, as an unsaturated compound having radical polymerization properties, polyfunctional acrylate, unsaturated polyester, etc., are widely investigated, and are industrially used. Various studies are conducted on such radical-polymerizable unsaturated compounds for the purpose of providing scratch resistance, stain resistance, etc., with their cured products. However, a composition obtained by mixing an organopolysiloxane compound, such as silsesquioxane, with a widely used radical-polymerizable unsaturated compound has disadvantages such that a uniform composition is hard to produce because of its poor compatibility, and that an organopolysiloxane compound is separated from the resulting cured product.
Patent Documents 1 to 5 disclose inventions relating to silsesquioxane having a radical-polymerizable functional group such as an acryloyloxy or methacryloyloxy group, and an ultraviolet curable composition containing the silsesquioxane. Such silsesquioxane-containing compositions have excellent heat resistance and scratch resistance; however, silsesquioxane has a problem such that its compatibility with other polymerizable unsaturated compounds, in particular, with polymerizable unsaturated compounds having high polarity is insufficient.